The invention relates to an exhaust gas unit for multicylinder diesel internal combustion engines with at least one particulate filter in the exhaust gas pipe and a regeneration device.
Because of the exhaust gas regulations to be expected for diesel internal combustion engines, to purify exhaust gas it will be necessary to place in the exhaust gas unit a particulate filter or soot filter that filters out the particulate and soot components in the exhaust gas. Thus, for multicylinder diesel internal combustion engines a particulate filter is necessary that has very large dimensions and is very expensive. If this large filter becomes damaged, for example due to clogging, the internal combustion engine and along with it the vehicle equipped with it are no longer able to function.
Arrangements where two particulate filters are arranged in parallel branches of an exhaust line and are alternately regenerable by gases produced by a burner, the outlet of which is selectively connectable to either branch of the exhaust line, is known from U.S. Pat. No. 4,345,431 and German Offenlegungsschrift No. 32 04 176. Now, if in a multicylinder diesel internal combustion engine two particulate filters are provided in the exhaust gas unit, the particulate filters of course can be made smaller and if one of the particulate filters fails the internal combustion engine and the vehicle equipped with it can still be operated, but difficulties relating to the filter operation result. If, for example, one of the filters is regenerated, then only the other filter is working in filter operation and the pressure on the one filter working in filter operation becomes so high that the engine operation is impaired. Even if one filter fails because it becomes damaged, the pressure occurring on the still remaining filter is too high for normal operation.
The object of the invention is thus to provide, while overcoming the difficulties described above, an exhaust gas unit for multicylinder diesel internal combustion engines of the type mentioned above that can be made at reasonable costs and, in the case of regeneration and damaging of a filter, at least a continued operation of the multicylinder diesel internal combustion engine and an operation of the vehicle is equips are assured.
According to the invention an exhaust gas unit for multicylinder diesel internal combustion engines with at least one particulate filter in the exhaust gas pipe and a regeneration device is distinguished in that at least four particulate filters are placed parallel to one another in the exhaust gas pipe. Since in the exhaust gas unit according to the invention at least four particulate filters are thus provided, the latter can be dimensioned relatively small, at least in diameter, so that the installation volume for the particulate filters, seen overall, is increased only insubstantially. Furthermore, such small-sized particulate filters can be produced at reasonable costs and can be placed in the exhaust gas pipe at a distance from the multicylinder diesel internal combustion engine at a suitable place.
Moreover, the design according to the invention obtains the advantage that, even when one of the filter fails, at least three parallel particulate filters are available for the filtering operation so that the multicylinder diesel internal combustion engine continues to operate almost unimpaired and a vehicle equipped with such an engine can continue to be operated. The pressure changes occurring in the exhaust gas unit due to the failure and/or shutting off for regeneration of any particular filter are relatively limited since the exhaust gas pressure to the filters remaining in operation does not increase very much.
Preferably, according to the invention, the design is made in such a way that a regeneration device in the form of a burner is assigned to each pair of filters and a flap is placed at the branching point to the particulate filters. With this configuration each pair of particulate filters, together with the assigned regeneration device, forms an independent, operable subcomponent group of the exhaust gas unit so that both parallel pairs of filters can operate and be regenerated, alternately and without influence of one on the other. Also, with this kind of design, essentially only one flap is needed per filter pair, which is preferably placed at the branching point to the particulate filters. To regenerate one of the filters of the filter pair, the filter to be regenerated can be uncoupled from the flow of exhaust gas by this flap and with the aid of the burner of the regeneration device the clogged filter is then freed of soot in that high temperature gases from the burner are supplied to heat the filter to the ignition temperature of the soot.
According to an advantageous further development according to the invention, which leads to a simplification with regard to the regeneration device, for the regeneration of all filters, a common burner is provided, a flap is placed at the branching points of each pair of filters, a common high temperature regeneration gas pipe that is connected to the burner outlet is connected to the branching points, and a flap is placed in the regeneration gas pipe to guide the regeneration gases from the burner to one of the pairs of filters. With this design, more flaps are required in the exhaust gas pipes leading to the particulate filters than in the previously explained configuration, specifically at least three, but for the regeneration of all filters only a single burner is needed in the exhaust gas unit.
Preferably, the burner(s) is/are operated, as a regeneration device in the exhaust gas unit, with exhaust gas from the exhaust gas line so that no great demands are placed on the airtightness of the flaps provided in the pipes leading to the filters, in a manner similar to that described in my copending U.S. patent application Ser. No. 196,558, filed May 20, 1988, claiming priority of German Patent Application No. P 37 17 140.2.
To operate the burner or burners with exhaust gas, there is connected to the burner(s) at least one exhaust gas feed pipe, which is connected to the exhaust gas manifold coming from the internal combustion engine upstream from the branching point to the particulate filters, and optionally, a flow volume control device, in the form of a flap, can be provided in this exhaust gas feed pipe. With such a design, when using a single common burner for all exhaust gas filters, or even when two burners are used, the burner(s) does/do not have exhaust gas from the exhaust line constantly flowing directly through it/them. Instead, only a limited amount is fed to the burner(s), especially when it/they is/are put into operation for regeneration.
According to a preferred configuration, the exhaust gas unit according to the invention is intended for a V-type multicylinder diesel internal combustion engine in which an exhaust gas pipe is assigned to each cylinder bank. Here, the design can be made in such a way that at least two particulate filters are placed in branches of each exhaust gas pipe and both exhaust gas pipes are connected to each other by a connecting pipe upstream of the point where the pipes branch to the particulate filters. This connecting pipe between the two exhaust gas pipes makes it possible that, in the case of regeneration of one of the filters, the exhaust gases, as a whole, can still go through at least three filters to prevent relatively large pressure changes and pressure increases being imposed on the filters. That is, the connecting pipe between the two exhaust gas pipes enables a flow distribution of the exhaust gases and a pressure equalization to occur, so that any one of the particulate filters can be regenerated without an appreciable impairment of the operation of the associated V-type multicylinder diesel internal combustion engine.
According to an alternative configuration, the exhaust gas unit according to the invention is intended for a multicylinder diesel internal combustion engine of the in-line type, in which usually only one exhaust gas pipe coming from the internal combustion engine is present. In this case, this exhaust gas pipe coming from the internal combustion engine is branched downstream from the cylinder bank into a pair of exhaust pipe sections which lead to a pair of branch pipes, within each of which a filter is placed. With such a design, in comparison to the preceding one, an additional connecting pipe can, of course, be dispensed with while still achieving essentially the same advantages. That is, one of the particulate filters can be regenerated without appreciably affecting the operation of the in-line multicylinder diesel internal combustion engine because no great pressure changes, especially pressure increases, result.
In particular, according to the invention, the design of the exhaust gas unit is made in such a way that the individual particulate filters are regenerated consecutively, so that only one of the at least four filters provided overall is uncoupled from filter operation during regeneration. As a result, at least three particulate filters are always available for purification of the exhaust gases.
Of course, instead of operating the burner of the regeneration device with exhaust gas, a burner can also be used that is fed with air from the atmosphere and then, of course, the flaps placed in the pipe system must be able to close in a completely airtight manner to guarantee reliable functioning of such a burner.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.